1. Field of the Invention
This invention relates to a motion conversion apparatus for converting a continuous rotational motion into a specific rotational motion, such as an intermittent rotational motion and a swinging rotational motion, or a motion of the predetermined type such as a combination of such rotational motions and a combination of such rotational motion and a rectilinear motion.
2. Related Art
Generally, a motion conversion apparatus comprises an input shaft connected to a driving device such as a motor, and an output shaft connected to a driven member such as a turntable or a conveyor, and a continuous rotational motion of the input shaft is converted to a motion of the output shaft through the cam mechanism, and this converted motion is transmitted to the driven member through the output shaft.
In such a motion conversion apparatus, during the positioning, a continuously-varying torque, acting on the output shaft during the positioning, as well as a reaction force of this torque, act as a fluctuation torque on the input shaft, thereby preventing the uniform rotation of the input shaft, so that the vibrations and a positioning error resulting therefrom develop during the positioning. Therefore, the motion conversion apparatus has been provided with a torque compensation device (as disclosed in Japanese Patent Unexamined Publication No. 54-159) so as to cancel the fluctuation torque of the input shaft which is produced by a conservative force such as an inertia force.
In this motion conversion apparatus, however, when a large fluctuation torque acts on the input shaft, an inertia body must be increased in accordance with this large fluctuation torque, and therefore the size of the apparatus may be increased. Therefore, as a method of effectively canceling such fluctuation torque, a torque compensation device of the air spring type as disclosed in Japanese Patent Unexamined Publication No. 1-120472 has been proposed.
This motion conversion apparatus produces a torque totally reverse to a fluctuation torque produced when a continuous rotational motion of an input shaft is converted into a motion of an output shaft, and this torque is caused to act on the input shaft, thereby canceling the produced fluctuation torque. The magnitude of the torque to be applied to the input shaft is adjusted by the positioning of a cam follower, engaged with a torque compensation cam provided in the apparatus and having a pre-calculated cam curve, and by a reciprocal movement of a piston moved in a cylinder in accordance with the movement of the cam follower. With this construction, the input shaft torque becomes uniform, and has a value close to zero throughout one cycle, that is, over the entire range of rotation of the input shaft through 360 degrees, and therefore adverse effects of the fluctuation torque in the motion conversion apparatus can be eliminated, and also the capacity of a drive motor can be reduced.
However, in the motion conversion apparatus disclosed in Japanese Patent Unexamined Publication No. 1-120472, attention is directed to the conserving energy such as the inertia load of the output shaft and the spring force acting on the output, and any consideration has not been given to the torque fluctuation due to a non-conserving, dissipating force such as a frictional force acting on the output shaft. Such frictional force is converted and dissipated by heat and so on, and this frictional force has heretofore been regarded as a necessary minimum energy loss, and there has heretofore existed no opinion that the fluctuation torque due to this frictional force should be compensated for. However, in some specific cam mechanisms, the frictional force is dominant, and can not be disregarded, and there is no conventional technique for dealing with such a case.